An increase in life expectancy has been accompanied by a larger number of patients with liver diseases that require surgical resection. The aged liver has significantly less reparative capacity following ischemia/ reperfusion (I/R) injury associated with this operation. Innovative approaches are urgently needed to reduce the age-dependent reperfusion injury and improve liver function of elderly patients following surgery. Mitochondrial dysfunction is the major mechanism precipitating lethal I/R injury to liver. Mitochondrial autophagy (mitophagy) is the cellular process that selectively removes abnormal mitochondria. The contribution of mitophagy to the age-dependent liver injury after warm ischemia is unknown. The goal of this study is to elucidate the mechanisms underlying the age-mediated lethal I/R injury to liver and to develop therapeutic strategies to improve liver function in the elderly patients after I/R. Our preliminary data demonstrate that the increased sensitivity of liver to I/R injury with age is strongly associated with its decreased mitophagic responsiveness. Preliminary results show that calpain-2-mediated loss of Atg4B, a key enzyme catalyzing the formation and recycling of autophagosomes, contributes to the age-dependent sensitivity of liver to I/R injury and mitochondrial dysfunction. In addition, we demonstrate that overexpression of Atg4B in both in vitro and in vivo models of I/R mitigates Atg4B loss, mitochondrial dysfunction and cell death. Thus, we propose that restoration or enhancement of mitophagy in aged liver will promote the clearance of dysfunctional mitochondria and consequently ameliorate liver dysfunction and bioenergetic failure after reperfusion. Our principal hypothesis is that defective or insufficient mitophagy is responsible for the increased sensitivity of old liver to lethal I/R injury. Two experimental models will be explored in this application using three different ages of mice. First, isolated hepatocytes will be utilized to determine the mechanisms of age-dependent mitophagic defects after I/R. Second, anesthetized mice will be employed to confirm and extend our I/R findings from an in vitro to an in vivo model. Finally, we will test the potential for mitophagy enhancing agents as therapeutic strategies to improve liver function after I/R in vivo. These studies provide critical mechanistic insights into the age-dependent I/R injury to liver, and will establish novel therapeutic approaches for improving I/R-mediated liver failure in the elderly patients.